This invention relates to specialty tubing and a method of manufacture of long lengths thereof for use, especially, in solar energy flat plate collectors. Such collectors are conventionally made of copper plates onto which copper tubes are soldered, or aluminum plates with aluminum tubes, or copper or aluminum "Rol-Bond" expanded tube-in-sheet. If copper is used for the fluid conduit, domestic water can be satisfactorily heated on a once-through basis. However, corrosion encountered with aluminum requires use of treated water on a recycled basis plus a intermediate heat exchanger. Copper tubes soldered to aluminum plate form a brittle soldered bond. However, aluminum is the preferred material of construction from the standpoint of cost and weight on the roof of a building.